naginterfaces.library.specfun.bessel_​i1_​scaled

naginterfaces.library.specfun.bessel_i1_scaled(x)

bessel_i1_scaled returns a value of the scaled modified Bessel function $e^{-\left|x\right|}{I}_1\left(x\right)$.

For full information please refer to the NAG Library document for s18cf

https://support.nag.com/numeric/nl/nagdoc_30/flhtml/s/s18cff.html

Parameters

xfloat

The argument $x$ of the function.

Returns

si1float

The value of the function at $x$.

Notes

bessel_i1_scaled evaluates an approximation to $e^{-\left|x\right|}{I}_1\left(x\right)$, where $I_1$ is a modified Bessel function of the first kind. The scaling factor $e^{-\left|x\right|}$ removes most of the variation in $I_1\left(x\right)$.

The function uses the same Chebyshev expansions as bessel_i1_real(), which returns the unscaled value of $I_1\left(x\right)$.

References

NIST Digital Library of Mathematical Functions